Field of the Invention
The present invention relates to a display device and a method for manufacturing the same, and more particularly, to a display device having a backlight unit with improved profile and efficiency.
Discussion of the Related Art
Stereoscopic image display devices may be divided into a stereoscopic technique and an autostereoscopic technique. The stereoscopic technique uses the parallex images of left and right eyes having a large stereoscopic effect, and includes a glasses technique and a glasses-free technique, both of which are in practical use.
The glasses technique displays right and left parallax images on a direct-view type display device or projector in an alternate manner and implements a stereoscopic image using polarized glasses or displays right and left parallax images in a time division manner and implements a stereoscopic image using shutter glasses.
The glasses-free technique divides the optical axes of right and left parallax images using an optical plate such as a parallex barrier, a lenticular lens sheet or switchable lens/barrier to implement a stereoscopic image. Due to its convenience of allowing the user to view a stereoscopic image without wearing shutter or polarized glasses, the glasses-free technique has been applied to small to medium-sized displays such as a smart phone, a tablet, a notebook, and the like in recent years.
A backlight unit of a display device employing such a glasses-free technique according to the related art will now be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic side view illustrating a display device having a backlight unit employing a glasses-free technique according to the related art.
Referring to FIG. 1, a glasses-free display device may include a wedge-type light guide plate 10 configured to change a light travelling direction, and a liquid crystal panel 20 disposed on an upper portion of the light guide plate 10 to implement an image through a light emitted from the light guide plate 10, and a LED light source array 30 disposed on a lateral surface of the light guide plate 10 to emit light into the light guide plate 10.
The wedge-type light guide plate 10 may include a thin end portion 10a corresponding proximately to the LED light source array 30, a thick end portion 10b corresponding to the thin end portion 10a, an outgoing light surface 10c in contact with the thin end portion 10a and thick end portion 10b to emit light toward the liquid crystal panel 20, and a bottom surface 10d formed with a plurality of step patterns 15 to correspond to the outgoing light surface 10c at a predetermined interval.
The thick end portion 10b of the light guide plate 10 is formed with a reflective curved surface 17, and the thin end portion 10a and outgoing light surface 10c are formed on a flat surface.
Referring to FIG. 2, the light emitted from the LED light source array 30 in a first direction may be guided to an inside of the wedge-type light guide plate 10 therethrough without meaningful loss, and the light reflected and propagated from the inside of the light guide plate 10 in a second direction is extracted from the light guide plate 10 to an outside thereof using the step patterns 15.
Referring back to FIG. 1, the light generated from the LED light source array 30 travels in the first direction to the thick end portion 10b along the length of the light guide plate from the thin end portion 10a of the light guide plate 10, and subsequently is reflected from the thick end portion 10b of the light guide plate 10. Then, when moving to the thin end portion 10a in the second direction along the length of the light guide plate, the light travels to the thin end portion 10a and at any position thereof along the length of the light guide plate, and is extracted from the light guide plate 10 through a mutual interaction with the step patterns 15. In other words, the light may be homogenized and extended while propagating in the first direction prior to being reflected from a non-flat surface, and extracted while propagating in the second direction.
The step patterns 15 of the light guide plate 10 may not substantially have an optical directional function for the light passing through the light guide plate from a first incident side to a second reflective side, thereby accomplishing a long rear working distance of the light reflective side as well as accomplishing a small thickness of the light guide plate.
FIG. 2 is a plan view illustrating a light guide plate for schematically explaining travelling states of light extracted through first and second light sources and a reflective curved surface of a backlight unit employing a glasses-free technique according to the related art. FIG. 3 is a simulation view schematically illustrating optical or light loss of a light guide plate of a backlight unit according to the related art.
Referring to FIG. 2, a beam 40 emitted from a first light source 30a in the wedge-type light guide plate 10 is directed to a first viewing window 60, and a beam 44 emitted from a second light source 30b is directed to a second viewing window 64 that is separated from the first viewing window 60 in a horizontal direction by the reflective curved surface 17 and step patterns 15 at the thick end portion 10b. 
In particular, the light emitted from two LED light sources 30a, 30b enters the thin end portion 10a of the wedge-type light guide plate 10, and then is diffused in a fan-shaped manner to the thick end portion 10b at an opposite side formed with the reflective curved surface 17, wherein the optical path of the diffused beams 40, 44 is converted and reflected on the reflective curved surface 17 in a substantially parallel manner (distant reflective focal length).
The beams 40, 44 reflected in a substantially parallel manner through the reflective curved surface 17 are sent to the first and the second viewing window 60, 64, respectively, in a planar light source form through the step patterns 15 formed on the bottom surface 10f to implement a three-dimensional image display.
However, forming special micro-patterns such as the step patterns 15 of the wedge-type light guide plate 10 has been difficult in commercialization and mass production and expensive due to its high failure rate of more than 90% with current technologies.
Also, the thickness of an upper bezel may increase due to a reflective curved surface formed on an outgoing light surface of the wedge-type light guide plate, thereby causing design restrictions. In addition, such a lower step pattern structure of the wedge-type light guide plate may require precise machining by, for example, an injection molding method. However, it may be difficult to manufacture such a wedge-type light guide plate by an injection molding method in large-sized production, and even if precise machining is possible, a crushing phenomenon of the step pattern structure at a micro level may occur when PMMA mold resin, for example, is injected into the mold frame.
Moreover, the wedge-type light guide plate according to the related art may suffer optical loss at a lower end portion as illustrated in FIG. 3, and a much larger optical loss may occur when a lower step pattern structure of the wedge-type light guide plate is not precisely machined.